1 files changed, 144 insertions, 0 deletions
diff --git a/src/main/java/org/openslx/virtualization/disk/DiskImageUtils.java b/src/main/java/org/openslx/virtualization/disk/DiskImageUtils.java
new file mode 100644
index 0000000..6bcef7f
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+++ b/src/main/java/org/openslx/virtualization/disk/DiskImageUtils.java
@@ -0,0 +1,144 @@
+package org.openslx.virtualization.disk;
+
+import java.io.IOException;
+import java.io.RandomAccessFile;
+
+/**
+ * Utilities to parse disk image format elements and control versions of disk images.
+ * 
+ * @author Manuel Bentele
+ * @version 1.0
+ */
+public class DiskImageUtils
+{
+	/**
+	 * Returns the size of a specified disk image file.
+	 * 
+	 * @param diskImage file to a disk storing the image content.
+	 * @return size of the disk image file in bytes.
+	 * 
+	 * @throws DiskImageException unable to obtain the size of the disk image file.
+	 */
+	public static long getImageSize( RandomAccessFile diskImage ) throws DiskImageException
+	{
+		final long imageSize;
+
+		try {
+			imageSize = diskImage.length();
+		} catch ( IOException e ) {
+			throw new DiskImageException( e.getLocalizedMessage() );
+		}
+
+		return imageSize;
+	}
+
+	/**
+	 * Reads two bytes ({@link Short}) at a given <code>offset</code> from the specified disk image
+	 * file.
+	 * 
+	 * @param diskImage file to a disk storing the image content.
+	 * @param offset offset in bytes for reading the two bytes.
+	 * @return value of the two bytes from the disk image file as {@link Short}.
+	 * 
+	 * @throws DiskImageException unable to read two bytes from the disk image file.
+	 */
+	public static short readShort( RandomAccessFile diskImage, long offset ) throws DiskImageException
+	{
+		final long imageSize = DiskImageUtils.getImageSize( diskImage );
+		short value = 0;
+
+		if ( imageSize >= ( offset + Short.BYTES ) ) {
+			try {
+				diskImage.seek( offset );
+				value = diskImage.readShort();
+			} catch ( IOException e ) {
+				throw new DiskImageException( e.getLocalizedMessage() );
+			}
+		}
+
+		return value;
+	}
+
+	/**
+	 * Reads four bytes ({@link Integer}) at a given <code>offset</code> from the specified disk
+	 * image file.
+	 * 
+	 * @param diskImage file to a disk storing the image content.
+	 * @param offset offset in bytes for reading the four bytes.
+	 * @return value of the four bytes from the disk image file as {@link Integer}.
+	 * 
+	 * @throws DiskImageException unable to read four bytes from the disk image file.
+	 */
+	public static int readInt( RandomAccessFile diskImage, long offset ) throws DiskImageException
+	{
+		final long imageSize = DiskImageUtils.getImageSize( diskImage );
+		int value = 0;
+
+		if ( imageSize >= ( offset + Integer.BYTES ) ) {
+			try {
+				diskImage.seek( offset );
+				value = diskImage.readInt();
+			} catch ( IOException e ) {
+				throw new DiskImageException( e.getLocalizedMessage() );
+			}
+		}
+
+		return value;
+	}
+
+	/**
+	 * Reads eight bytes ({@link Long}) at a given <code>offset</code> from the specified disk image
+	 * file.
+	 * 
+	 * @param diskImage file to a disk storing the image content.
+	 * @param offset offset in bytes for reading the eight bytes.
+	 * @return value of the eight bytes from the disk image file as {@link Long}.
+	 * 
+	 * @throws DiskImageException unable to read eight bytes from the disk image file.
+	 */
+	public static long readLong( RandomAccessFile diskImage, long offset ) throws DiskImageException
+	{
+		final long imageSize = DiskImageUtils.getImageSize( diskImage );
+		long value = 0;
+
+		if ( imageSize >= ( offset + Long.BYTES ) ) {
+			try {
+				diskImage.seek( offset );
+				value = diskImage.readLong();
+			} catch ( IOException e ) {
+				throw new DiskImageException( e.getLocalizedMessage() );
+			}
+		}
+
+		return value;
+	}
+
+	/**
+	 * Reads a variable number of bytes (<code>numBytes</code>) at a given <code>offset</code> from the specified disk image file.
+	 * 
+	 * @param diskImage file to a disk storing the image content.
+	 * @param offset offset in bytes for reading <code>numBytes</code> bytes.
+	 * @param numBytes number of bytes to read at <code>offset</code>.
+	 * @return read bytes from the disk image file as {@link byte[]}.
+	 * 
+	 * @throws DiskImageException unable to read bytes from the disk image file.
+	 */
+	public static byte[] readBytesAsArray( RandomAccessFile diskImage, long offset, int numBytes )
+			throws DiskImageException
+	{
+		final long imageSize = DiskImageUtils.getImageSize( diskImage );
+		byte values[] = {};
+
+		if ( imageSize >= ( offset + numBytes ) ) {
+			try {
+				diskImage.seek( offset );
+				values = new byte[ numBytes ];
+				diskImage.readFully( values );
+			} catch ( IOException e ) {
+				throw new DiskImageException( e.getLocalizedMessage() );
+			}
+		}
+
+		return values;
+	}
+}